A finding of two unfused primary ossification centers, as indicated by staining, usually resulting in two separate and distinct bones.

Ossification centers not fused. Commonly used for structures arising from two or more primary ossification centers (e.g., sternebrae, vertebral centra). Applies only to the ossification sites and does not imply that the structure, as represented by the bone precursor, is divided (split). (Makris S, Solomon HM, Clark R, Shiota K, Barbellion S, Buschmann J, Ema M, Fujiwara M, Grote K, Hazelden KP, Hew KW, Horimoto M, Ooshima Y, Parkinson M, Wise LD. Terminology of developmental abnormalities in common laboratory mammals (Version 2). Part B. Birth Defects Res B Dev Reprod Toxicol. 2009 Aug;86(4):227-327.)